The present invention relates to an apparatus for the anaerobic filtration of waste water with the simultaneous production of biogas, and specifically to the type of such apparatus provided with a filling material which is infiltrated from the bottom to the top by the water to be treated.
More particularly, a submerged filter embodying the principles of the invention can be used for the treatment of industrial waste water with heavy carbonaceous polution such as waste water from agro-alimentary industries, fermentation industries, synthetic chemical industries, paper pulp industries, etc., permitting the production of considerable amounts of biogas, i.e. from 0.4 to 0.6 m.sup.3 per kg of eliminated Chemical Oxygen Demand (COD).
Various devices of this general type are well known in the art and include anaerobic filters containing a filling material made of plastic and through which passes from bottom to top the waste water to be treated. Such filters generally can be classified into two groups.
In one known group, a filter contains a filling material such as loosely packed plastic rings. This loose packing permits rapid colonization of the waste material by the anaerobic microorganisms and a considerable accumulation of biomass, and thus is an effective treatment. However, with this type of filter there is the considerable danger that the filter will become clogged, thereby causing the material to become compacted. Moreover, the specific surface, i.e. the surface area per ring volume, often is inadequate, particularly if the filter is in the form of plastic rings with a large diameter, thus causing the material to become compacted.
A filter of the other prior art group includes an ordered filling material, for example tubes or corrugated plates of plastic material, such as known by the various trade names "Cloisonyle", "Plasdek", etc. This arrangement substantially eliminates the danger of clogging, but has other drawbacks, namely the colonization of the material by the micro-organisms is very slow, and there is the danger that the fixed culture will become disengaged upon the occurrence of sudden changes in operating conditions, i.e. pressure and velocity of flow.